1. Field of the Invention
This invention pertains to foldable booms, and more particularly, it relates to agricultural spray booms or the like which extend laterally of a propelling vehicle and which must be capable of yielding when they strike objects such as trees or fences, etc.
2. Description of the Prior Art
It is well known in the art to pivotally mount an outer boom wing to a rigid inner boom structure and to permit the boom wing to pivot in either direction out of its desired transverse spraying position in response to being contacted by an abutment such as a post or tree. U.S. Pat. No. 2,541,417, which issued to Hartsock on Feb. 13, 1951, discloses such an arrangement. The patentee provides a pair of springs of equal force which are connected to opposite sides of the wing to return the wing to its transversely extending position after being contacted by and moved past an abutment. It is known, however, that the effective spring rate of the double spring arrangement is zero at the transversely extended, or neutral, position. Thus, the wing may be deflected from its neutral position with little force resulting in possible swaying of the wing during the spraying operation causing an uneven application of spray on the plants being treated.
U.S. Pat. No. 2,770,493, which issued to Fieber on Nov. 13, 1976, discloses the use of taut elastic cables and a spring for maintaining a spray boom in its desired spraying position. The structure is not designed for yieldable movement to clear obstacles, however; nor is it designed to be folded inwardly when the boom is to be transported.
U.S. Pat. No. 3,329,030, which issued to Dijkhof on July 4, 1967, shows that it is old to provide a two-piece boom which may be moved from a transversely extending operative position to a folded transport position. The patentee uses a chain and sprocket drive for pivoting the two-piece boom between such two positions, which drive causes the boom structure to act as a rigid one-piece unit when in the extended position.